This invention is directed to containers and is particularly directed to a shipping and storage container for spent fuel elements of nuclear reactors.
It is the practice in the operation of nuclear reactors to change approximately one-third of the nuclear fuel elements of a reactor each year. These fuel elements comprise a subassembly, or bundle, of fuel rods. The fuel elements of a boiling water reactor (BWR) are normally 51/2" square by 176" long. The fuel elements of a pressurized water reactor (PWR) are approximately 81/2" square and 164" long.
When removed from the reactor, these spent fuel assembles are still highly radioactive. Consequently, care must be taken to ensure that the container in which the elements are stored and shipped does not permit escape of excessive radiation. Moreover, the spent fuel elements generate heat incident to their radioactive decay. For example, a so-called "5-year cool down" PWR fuel element generates 100 kilowatts of heat when removed, 12 kilowatts 90 days after removal and one kilowatt after five years. Similarly, a BWR fuel element generates 50 kilowatts when removed, six kilowatts 90 days after removal, and is still generating one-half kilowatt five years after removal. Consequently, the cask must provide for effective heat dissipation to prevent the fuel assemblies or portions of the cask from deteriorating in any way that could cause escape of radioactive or toxic substances.
Another requirement of spent fuel casks is that they be rugged and able to withstand the jarring and bumping incident to transportation by truck or rail without structural damage which might permit the escape of radioactive gases or other contaminants. Such casks must also meet the stringent requirements of the 10 C.F.R. part 71 specified accident criteria.